1. Technical Field
The present invention relates to a spectacle lens, a spectacle lens design method, and a design apparatus.
2. Related Art
Correcting average power with respect to prescribed power, that is, reducing an average power error, and reducing astigmatism are at least two essential requirements to design a spectacle lens that provides a clear field of view. For example, JP-A-2003-215507 describes providing a spectacle lens having a shallow base curve and capable of suppressing not only an average power error and astigmatism but also distortion. The spectacle lens described in JP-A-2003-215507 has a spherical outer surface and a rotationally symmetric aspherical inner surface. Further, an average power error and astigmatism are primarily corrected in a central portion where the viewing angle ranges from 0 to 30 degrees, and distortion is primarily corrected in a peripheral portion. When an object is viewed through the lens described above, a clear image is provided across the range over which the eyeball moves and a distortion-corrected image is formed in a peripheral portion of the retinal, whereby the wearer enjoys a satisfactory field of view. JP-A-2003-215507 describes that an average power error, astigmatism, and distortion are not necessarily corrected across the lens but the weighted aberration correction described above ensures satisfactory optical performance recognizable by the wearer, whereby satisfactory optical performance is achieved and a shallow base curve for reducing the thickness of the lens can be employed at the same time.
The spectacle lens described in JP-A-2003-215507, which provides a clear image through the central portion of the lens, however, has a disadvantage of insufficient astigmatism correction in the peripheral portion of the lens, which can result in a distorted, unclear image formed through the peripheral portion. The distortion of an image formed through the peripheral portion may reduce performance in use and make the lens less fashionable, for example, may distort the contour of the face of the wearer (person who wears eyeglasses) viewed through the lens.
Eyeglasses are not only an important medical tool that aids vision but also an important fashion item on which the impression of the wearer depends. It is therefore desired to develop eyeglasses and a spectacle lens that are easy to use and highly fashionable.